1. Field of the Invention
This invention relates generally to orthopedic knee braces and, more particularly, to a dynamic knee brace that uses muscle power to apply a bending force across a knee.
2. Description of Related Art
Unicompartmental osteoarthritis is a condition where the cartilage on one compartment of the knee has worn away more than the other compartment. This damage to the compartment on one side of the knee causes increased pressure on the damaged compartment, which may be severe enough to be visible as a change in the angulation of the joint. This makes it painful for the patient to engage in activities where there is a load being applied to the knee, such as waking or even standing. Unicompartmental osteoarthritis is generally treated by shifting the load applied across the knee to the compartment that has the least amount of damage, thereby opening the damaged compartment.
If there is also a deformity in the knee joint, a high tibial osteotomy can be used to realign the joint and shift the load to the undamaged compartment in the knee. A high tibial osteotomy is a surgical procedure that involves cutting a triangular section off the top of the tibia to realign the joint and open the damaged compartment. After this procedure, it is important to protect the leg to ensure that the bones heal together properly. This is often accomplished by placing the leg in a cast. However, since it is beneficial to allow the knee to pivot during the healing process, a brace can be used to hold the leg in the desired configuration while allowing the knee to freely pivot. If a brace is used after a high tibial osteotomy, the brace arms are often bent to the desired inclination to hold the leg in the desired configuration and provide the necessary support.
A knee brace may also be used without surgery, in order to treat unicompartmental osteoarthritis. This is accomplished by providing a bending force across the knee to hold open the damaged compartment of the knee. A three-point bending force is accomplished by having a force applied to the knee on the side opposite from the damaged compartment. This is often done using a strap, a condoyle pad, or other such instrumentality. The force against the knee is countered by two brace arms, which provide static forces against the leg above and below the knee. The brace arms can be bent or otherwise inclined toward the leg using known joints in order to increase the force across the knee. By pulling the knee against the brace arms, the brace applies a three-point bending force at the knee to open the damaged compartment. Alternatively, a four-point bending force can be utilized by applying a force just above and below the knee instead of applying a single force directly to the knee. This avoids applying pressure directly at the knee but creates an equivalent bending moment at the knee as a three-point bending force.
A major disadvantage of most braces for treating unicompartmental osteoarthritis is that they provide a static bending force across the knee, which does not change as the knee moves between flexed and extended positions. The pressure in the damaged compartment increases, thereby causing pain, only when weight is being applied to the leg. This occurs close to or at full extension of the knee. The application of force when the knee is partially flexed can make the brace uncomfortable to wear. In addition, when the knee is partially flexed applying a bending force across the knee results in a rotational force that results in a tendency of the brace to rotate around the leg, which lessens its effectiveness. This tendency to rotate increases with the amount of force applied, thereby preventing static force braces from applying the forces required to treat more severe cases of unicompartmental osteoarthritis.
Applicant has previously provided a dynamic brace that overcomes this problem, called the Thruster brace, which has been successfully marketed by Medical Technology, Inc. of Grand Prairie, Tex. The Thruster brace only applies the bending force as the knee nears full extension and completely removing it as the knee bends back to a flexed position. It has two brace arms that are connected together by a central polycentric joint that allows the knee to pivot. A hinge in each brace arm allows each brace arm to incline in a medial/lateral direction. Two cams are positioned over the central joint with cam surfaces facing each other and cam followers on the other end of each cam. As the knee moves to extension, the cam surfaces on each assembly contact and roll along each other, and due to the shape of the cams, push the corresponding cam followers away from the central joint.
At some point as the knee moves to full extension, the cam followers contact the end of a timing screw extending from an adjustment block located on each brace arm. Further extension of the knee pushes the cam follower further toward the adjustment block, resulting in the brace arm being pushed around the medial/lateral joint toward the leg into a particular degree of inclination. The timing of when the cam follower first contacts the adjustment block, and thus the total amount of inclination that is achieved at full extension, is determined by how far the adjustment screw is threaded through each of the adjustment blocks. While this brace has achieved significant results, there is still opportunity for improvement of dynamic braces.